As the world's population expands and its economy increases, the atmospheric concentrations of carbon dioxide are warming the earth, causing climate change. However, the global energy system is moving steadily away from the carbon-rich fuels whose combustion produces carbon dioxide gas. Experts say atmospheric levels of carbon dioxide may be double that of the pre-industrial era by the end of the next century, but they also say the levels would be much higher except for a trend toward lower-carbon fuels that has been going on for more than 100 years. Furthermore, fossil fuels cause pollution and are a causative factor in the strategic military struggles between nations. Furthermore, fluctuating energy costs are a source of economic instability worldwide.
In the United States, it is estimated, that the trend toward lower-carbon fuels combined with greater energy efficiency has, since 1950, reduced by about half the amount of carbon spewed out for each unit of economic production. Thus, the decarbonization of the energy system is the single most important fact to emerge from the last 20 years of analysis of the system. The present invention is another product which is essential to shortening the period of decarbonization. It is expected, hydrogen will be used in fuel cells for cars, trucks and industrial plants, just as it already provides power for orbiting spacecraft. But, with the problems of storage and infrastructure solved (see U.S. application Ser. No. 09/444,810, entitled “A Hydrogen-based Ecosystem” filed on Nov. 22, 1999 for Ovshinsky, et al., which is herein incorporated by reference and U.S. patent application Ser. No. 09/435,497, entitled “High Storage Capacity Alloys Enabling a Hydrogen-based Ecosystem”, filed on Nov. 6, 1999 for Ovshinsky et al., which is herein incorporated by reference), hydrogen will also provide a general carbon-free fuel to cover all fuel needs. Utilizing the inventions of subject assignee, the hydrogen can be stored and transported in solid state form in trucks, trains, boats, barges, etc. (see the '810 and '497 applications).
A fuel cell is an energy-conversion device that directly converts the energy of a supplied gas into an electric energy. Researchers have been actively studying fuel cells to utilize the fuel cell's potential high energy-generation efficiency. The base unit of the fuel cell is a cell having an oxygen electrode, a hydrogen electrode, and an appropriate electrolyte. Fuel cells have many potential applications such as supplying power for transportation vehicles, replacing steam turbines and power supply applications of all sorts. Despite their seeming simplicity, many problems have prevented the widespread usage of fuel cells.
Presently most of the fuel cell R & D focus is on P.E.M. (Proton Exchange Membrane) fuel cells. The P.E.M. fuel cell suffers from relatively low conversion efficiency and has many other disadvantages. For instance, the electrolyte for the system is acidic. Thus, noble metal catalysts such as platinum and palladium are the only useful active materials for the electrodes of the system. Unfortunately, not only are the noble metals costly, they are also susceptible to poisoning by many gases, and specifically carbon monoxide (CO). The proton exchange membrane itself is quite expensive, and because of its low conductivity, inherently limits the power performance and operational temperature range of the P.E.M. fuel cell (the P.E.M. is nearly non-functional at low temperatures, unlike the fuel cell of the instant invention). Also, the membrane is sensitive to high temperatures, and begins to soften at 120° C. The membrane's conductivity depends on water and dries out at higher temperatures, thus causing cell failure. Therefore, there are many disadvantages to the P.E.M. fuel cell which make it somewhat undesirable for commercial/consumer use.
The conventional alkaline fuel cell has some advantages over P.E.M. fuel cells such as higher operating efficiencies, use of less expensive materials of construction, and no need for expensive membranes. The alkaline fuel cell also has higher ionic conductivity electrolyte, therefore it has a much higher power capability. Unfortunately, conventional alkaline fuel cells still suffer from certain disadvantages. For instance, conventional alkaline fuel cells still use expensive noble metals catalysts in both electrodes, which, as in the P.E.M. fuel cell, are susceptible to gaseous contaminant poisoning and dominate cost of manufacture. While the conventional alkaline fuel cell is less sensitive to temperature than the P.E.M. fuel cell, the active materials of conventional alkaline fuel cell electrodes become very inefficient at low temperatures.
Fuel cells, like batteries, operate by utilizing electrochemical reactions. Unlike a battery, in which chemical energy is stored within the cell, fuel cells generally are supplied with reactants from outside the cell. Barring failure of the electrodes, as long as the fuel, preferably hydrogen, and oxidant, typically air or oxygen, are supplied and the reaction products are removed, the cell continues to operate.
Fuel cells offer a number of important advantages over internal combustion engine or generator systems. These include relatively high efficiency, environmentally clean operation especially when utilizing hydrogen as a fuel, high reliability, few moving parts, and quiet operation. Fuel cells potentially are more thermodynamically efficient than other conventional power sources based upon the Carnot cycle.
The major components of a typical fuel cell are the hydrogen electrode for hydrogen oxidation and the oxygen electrode for oxygen reduction, both being positioned in a cell containing an electrolyte (such as an alkaline electrolytic solution). Typically, the reactants, such as hydrogen and oxygen, are respectively fed through a porous hydrogen electrode and oxygen electrode and brought into surface contact with the electrolytic solution. The particular materials utilized for the hydrogen electrode and oxygen electrode are important since they must act as efficient catalysts for the reactions taking place.
In an alkaline fuel cell, the reaction at the hydrogen electrode occurs between hydrogen fuel and hydroxyl ions (OH−) present in the electrolyte, which react to form water and release electrons:H2+2OH−→2H2O+2e−.At the oxygen electrode, oxygen, water, and electrons react in the presence of the oxygen electrode catalyst to reduce the oxygen and form hydroxyl ions (OH−):O2+2H2O+4e−→4OH−.The flow of electrons is utilized to provide electrical energy for a load externally connected to the hydrogen and oxygen electrodes.
The catalyst in the hydrogen electrode of the alkaline fuel cell has to not only split molecular hydrogen to atomic hydrogen, but also oxidize the atomic hydrogen to release electrons. The overall reaction can be seen as (where M is the catalyst):M+H2→2MH→M+2H++2e−.Thus the hydrogen electrode catalyst must efficiently dissociate molecular hydrogen into atomic hydrogen. Using conventional hydrogen electrode material, the dissociated hydrogen atoms are transitional and the hydrogen atoms can easily recombine to form molecular hydrogen if they are not used very quickly in the oxidation reaction. With the hydrogen storage electrode materials of the inventive instant startup fuel cells, the atomic hydrogen is immediately captured and stored in hydride form, and then used as needed to provide power.
The use of precious metals as catalyst material is prevalent in current fuel cells. Many fuel cells, such as Proton Exchange Membrane (PEM) fuel cells use platinum as the catalytic material within the positive and negative electrodes. While platinum may work well under certain conditions, the use of platinum may result in cost problems for the wide scale production of fuel cells in the years to come. Platinum is currently available for the limited production of fuel cells, but wide scale production of fuel cells utilizing platinum will substantially increase the price and demand for platinum, which will cause the price of fuel cells to be unaffordable for the public resulting in the halt or decrease of fuel cell production. To make fuel cells readily available to the public at affordable prices, alternatives to platinum must be utilized within the fuel cells without a compromise in performance.
Current fuel cells such as PEM, Methanol, Phosphoric Acid, Molten Carbonate, and Solid Oxide, have difficulty operating at ambient temperatures without the use of a heating systems. Of the fuel cells previously listed, PEM and methanol fuel cells have the lowest operating temperature at around 75° C. The other fuel cells have operating temperatures beyond 210° C. High operating temperatures provide design problems when trying to utilize these fuel cells in applications requiring operating conditions at ambient or lower temperatures, such as utilization in automobiles. Heat must be continually supplied to these fuel cells upon startup and during operation to maintain operation. This temperature dependence is detrimental to the wide scale use of fuel cells in a variety of applications operating at ambient temperatures. For fuel cells to gain acceptance as a viable source of power for automobiles, generators, power packs, and the like, fuel cells must be able to operate in a variety of conditions, including low temperatures. The ability for fuel cells to operate at low temperatures is a criteria that is essential for fuel cells to gain acceptance as a viable source of power for a wide variety of applications.